February R&D Round Up

E-mail Melanie Martella

This month's round up is peculiarly rich in both energy harvesting and tininess, with a millimeter-scale, solar-powered sensor system developed at the University of Michigan, small wireless sensor nodes that can keep track of small objects, courtesy of CSIRO in Australia, and another step toward battery-less radios courtesy of Imec and Holst Centre.

Small, Solar-Powered Sensor System
What's 2.5 by 3.5 by 1 mm and includes a microprocessor, battery and solar cells? That would be the sensor system develop at the University of Michigan. The device incorporates an ARM Cortex-M3 processor, a Cymbet thin-film battery, and some very creative power management methods to get the total average power consumption down to <1 nW. Yes, that's right, <1 nW. Like most other small-scale autonomously powered sensor systems, the system spends most of its time in sleep mode, waking up every couple of minutes to take measurements.

The processor takes 0.5 V to operate but the battery provides almost 4 V. Rather than using traditional, power-hungry voltage conversion methods to throttle that back and thus ensure the most efficient processor operation, the team instead slowed the unit clock of the power management unit in response to light processor loads. The power frugality exhibited by the system holds promise for medical applications—biomedical monitoring that is implantable and that can power itself from temperature differences or other energy sources within the body—and, according to the article "Millimeter-scale, energy-harvesting sensor system developed," from the University of Michigan News Service, the inventors are in fact working to commercialize the device.

Sensor Nodes to Track Your Stuff
CSIRO, the Australian national science agency, has a long history with ad hoc wireless sensor networking. Researchers created the FLECK wireless sensor nodes for environmental monitoring. The original FLECK nodes were designed to be capable of using solar power, have a range of up to 1 km, be low power, and to offer a range of sensors and sensor interfaces.

The latest generation of devices are the FLECK Nano nodes that are 25 by 20 mm in size, have an indoor range of 7–20 m, and incorporate a triaxial accelerometer, an 8051 microcontroller, and a 915 MHz transceiver. Students at CSIRO are applying these smaller nodes indoors. By tagging various office objects, the students seek to discover how ubiquitous sensing plays out in an office environment. Not only are the nodes capable of monitoring the indoor environment for temperature and power use, among other things, but they could also be used to track objects unobtrusively. You can read more in the article, "Students find lost office gear with tiny sensors." Mind you, there'd be no more question of where your red Swingline stapler has wandered off to if you've got this system in place!

A Boost for Battery-less Radios
In another impressive gain in the low-power wireless arena, researchers at Imec and Holst Centre have developed a 2.4 GHz/915 MHz wake-up receiver that consumes 51 µW of power. The tiny radio (0.36 by 0.36 mm) has a novel architecture that uses double sampling to combat noise and to boost sensitivity with increasing data rate.

The work is part of the research organizations' goal of developing wireless autonomous sensor systems, and an integral step toward attaining that goal is to develop systems where the DPS, radio, and sensor draw only 100 µW and are thus suited to battery-less or energy-scavenging operation. To learn more please read the article "Imec and Holst Centre achieve breakthrough in battery-less radios".

One thing that I note about many of these projects to salt our environment with tiny, autonomous sensors, is that they don't necessarily discuss what to do with the vast quantities of data that will be generated. It should be fascinating to watch how this issue gets handled once the technology is out of the lab and into the world.